Objective Adolescence is a critical period of transition from paediatric to adult health care, but readiness for this transition has been described as low in the general adolescent population. We aimed to investigate whether transition readiness improved over time among US adolescents and to examine associations between demographic and clinical characteristics and transition readiness over time. Methods Deidentified caregiver‐reported repeated cross‐sectional data from the 2016–2020 National Survey of Children's Health were analysed for caregiver‐reported measures of transition readiness among adolescents age 12–17 years. Logistic regression was used to identify trends in transition readiness and change over time in factors associated with this outcome. Results Among 55 022 adolescents represented in the five survey years, the proportion meeting a composite definition of transition readiness increased from 15% (95% confidence interval [CI]: 14%, 16%) in 2016 to 19% (95% CI: 17%, 20%) in 2020. After multivariable adjustment, each additional year was associated with 12% greater odds of caregiver‐reported transition readiness (95% CI: +8%, +15%; P < 0.001), and transition readiness was more likely for girls, older adolescents and adolescents with special health care needs. Associations between adolescent characteristics and transition readiness did not change over the study period. Conclusions Population‐level caregiver‐reported transition readiness among US adolescents has increased but remains low. Factors previously associated with transition readiness (age, sex, race and ethnicity, family income and presence of special health care needs) have persisted over recent years.